1. Field of the Invention
The present invention relates to a combusting system, a remodeling method for the combusting system, and a fuel injection method for the combusting system.
2. Description of the Related Art
Japanese Unexamined Patent Application Publication No. 10-121986 (Patent Publication 1) discloses a gas turbine including multiple combustors. Generally, gas turbines of the type including multiple combustors are each configured such that all adjacent combustors disposed annularly along the perimeter of the gas turbine are fluidly connected to one another through a cross fire tube. The cross fire tube allows combustion gases to flow through the inside thereof by making use of the inter-combustor pressure difference. Of the multiple combustors, one or two combustors are each provided with a ignitor that generates electrical spark.
Starting of the gas turbine causes the rotation speeds of a compressor to be increased with external energy, thereby causing air to be introduced into the combustor. Thereafter, upon generation of an ignition instruction signal, sparking is started by the ignitor, a fuel control valve is opened, and the fuel is supplied concurrently to all combustors. Then, the combustor including the ignitor is first ignited. Upon ignition, the pressure difference occurs between interior spacings of internal cylinders of the ignited ignitor and an un-ignited combustor. Hence, combustion gases at high temperature enter the un-ignited combustor, and the un-ignited combustor is responsively ignited with thermal energy generated thereby. This operation is performed sequentially in the adjacent combustors, and all the combustors are ignited.
However, with a gas turbine of the above-described type including multiple combustors, there occur problems such as described below during the ignition of the combustors.
In the configuration including multiple combustors, the ratio between fuel and air necessary for ignition (“ignition fuel-air ratio,” herebelow) is relatively higher in ignition using thermal energy of combustion gases entering from the adjacent combustor (“cross fire ignition,” herebelow), as compared to the air-to-fuel ratio in ignition in the presence of or with the ignitor (“spark plug ignition,” herebelow). Hence, in a gas turbine combustor in which the fuel supply timing is identical in each of all combustors, even when high temperature combustion gases enter the adjacent combustor from the combustor ignited with the ignitor, a necessary amount of fuel for the cross fire ignition is not supplied. As a result, ignition failure can occur.
In particular, in many cases, in the event of ignition of the ignitor-equipped combustor, a large volume of combustion gases is caused to enter the adjacent combustor due to an abrupt pressure rise in the combustor, and then ignition occurs. Hence, the time required until the occurrence of ignition of all the combustors is about several seconds. As such, it is considered that the timing of ignition of the ignitor-equipped combustor and the timing of reaching of the adjacent un-ignited combustor to a target fuel flow amount greatly influence.